Allograft bone is a graft substitute readily available from cadavers and avoids the surgical complications and subject morbidity associated with harvesting autologous bone. Allograft bone is essentially a load-bearing matrix comprised of cross-linked collagen, hydroxyapatite, and osteoinductive Bone Morphogenetic Proteins (BMP). Human allograft tissue is widely used in orthopedic surgery. Allograft tissue is strong, integrates with the recipient host bone, and can be shaped either by the surgeon to fit the specific defect or shaped commercially by a manufacturing process. Allograft bone is available in two basic forms: cancellous and cortical. Cortical bone is a highly dense structure comprised of triple helix strands of collagen fiber reinforced with hydroxyapatite. The hydroxyapatite component is responsible for the high compressive strength and stiffness of bone while the collagen fiber component contributes to its elastic nature, as well as torsional, shear, and tensile strength. Cortical bone is the main load-bearing component of long bones in the human body.
Use of allograft material is often a preferred treatment option for musculoskeletal related injuries. Significant problems associated with the use of allografts are recipient rejection of the tissue due to the presence of donor related antigens still present in the allograft, allograft inability to incorporate into the host, and contaminated tissue used in transplant. Numerous methodologies have been employed to reduce the level of antigenic compounds present in allografts and perform low-level disinfection and sterilization. These methods generally include numerous washes with a variety of chemicals. These methods have extreme drawbacks to the extent that they utilize reactive chemicals that alter the structural components of the allograft or denature and/ or remove compounds that facilitate integration of the allograft by the recipient.
It therefore would be highly desirable if a sterilization method could be provided leading to improved clincal outcomes of bone grafting.
Recently, in U.S. Pat. No. 6,149,864 to Dillow et al and U.S. Pat. No. 7,108,832 to Christensen et al. (the entire content of both are expressly incorporated herein by reference), the use of supercritical CO2 was disclosed as an alternative to existing technologies for sterilizing a wide range of products for the healthcare industry with little or no adverse effects on the material treated.